Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers

BACKGROUND

Animal and in vitro studies have provided evidence of an anticarcinogenic effect of active ingredients in garlic.

OBJECTIVE

The objective was to conduct meta-analyses of the epidemiologic literature on the association between garlic consumption and risk of stomach, colon, head and neck, lung, breast, and prostate cancers.

DESIGN

Meta-analyses were conducted for all cancers mutually and separately for colorectal and stomach cancers in relation to consumption of exclusively raw garlic, cooked garlic, or both (RC garlic). Eighteen studies reported a relative risk estimate for RC garlic consumption and cancer risk.

RESULTS

In the meta-analyses of colorectal and stomach cancer, the reference categories ranged from no consumption to consumption of 3.5 g/wk, whereas the highest categories ranged from any consumption to >28.8 g/wk. The average difference between the highest and lowest categories was 16 g/wk. The random-effects relative risk (RR) estimate of colorectal cancer and RC garlic consumption, excluding garlic supplements, was 0.69 (95% CI: 0.55, 0.89). For stomach cancer, the random-effects RR estimate was 0.53 (95% CI: 0.31, 0.92). The heterogeneity among studies for the latter outcome (P: = 0.0002) indicates the questionableness of the generalizability of this summary estimate. An indication of publication bias for all cancers combined is evident from a funnel plot of RC garlic consumption and cancer risk and from the results of the Begg and Mazumdar test (P: = 0.049).

CONCLUSIONS

High intake of RC garlic may be associated with a protective effect against stomach and colorectal cancers. Heterogeneity of effect estimates, differences in dose estimation, publication bias, and possible alternative hypotheses (eg, confounding by total vegetable consumption) preclude sole reliance on summary effect estimates.

Mechanisms by which garlic and allyl sulfur compounds suppress carcinogen bioactivation. Garlic and carcinogenesis

Overall, a host of studies provides compelling evidence that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. These studies reveal that the benefits of garlic are not limited to a specific species, to a particular tissue, or to a specific carcinogen. Several mechanisms are likely to account for this protection. Notable among these is a depression in nitrosamine formation and a reduction in carcinogen bioactivation. The benefits provided by garlic must be viewed as part of the entire diet, since several dietary constituents can influence the degree of protection. More than one compound is responsible for the anticancer properties associated with garlic. Future research should focus on how genetic variability and daily environmental factors influence the anticancer benefits attributed to garlic and its allyl sulfur components.

Neurotrophic activity of organosulfur compounds having a thioallyl group on cultured rat hippocampal neurons

Several organosulfur compounds found in garlic extract promoted the survival of rat hippocampal neurons in vitro. From the analysis of structure-activity relationship, thioallyl group in these compounds is essential for the manifestation of neurotrophic activity. S-Allyl-L-cysteine (SAC), one of the organosulfur compounds having thioallyl group in garlic extract, also promoted the axonal branching of cultured neurons. These results suggest that thioallyl compounds make a unique group of neurotrophic factors.

Influence of oryzanol on platelet aggregation in rats

Platelet aggregation was measured using platelet rich plasma prepared from rats fed oryzanol in the control diet and those fed oryzanol in a 1 per cent cholesterol diet (HCD). Oryzanol with the control diet did not alter platelet aggregation induced by ADP and collagen. On the other hand, oryzanol fed along with HCD significantly inhibited platelet aggregation induced by ADP and totally inhibited aggregation induced by collagen.

A protein fraction from aged garlic extract enhances cytotoxicity and proliferation of human lymphocytes mediated by interleukin-2 and concanavalin A

Fraction 4 (F4), a protein fraction isolated from aged garlic extract, enhanced cytotoxicity of human peripheral blood lymphocytes (PBL) against both natural-killer (NK)-sensitive K562 and NK-resistant M14 cell lines. Although F4 treatment alone increased cytotoxicity, the effect was more remarkable when F4 was administered together with suboptimal doses of interleukin-2 (IL-2); combination treatment of 5 micrograms/ml F4 plus 10 U/ml IL-2 for 72 h generated lymphokine-activated killer activity equivalent to that produced by 100 U/ml IL-2 alone against M14. F4 enhanced IL-2-induced proliferation and IL-2 receptor (Tac) expression of PBL without significant increase of IL-2 production. The enhancement of cytotoxicity both by F4 alone and by F4 plus IL-2 was abolished by anti-IL-2 antibody. F4 also enhanced concanavalin-A(ConA)-induced proliferation of PBL. Radiolabeled-ConA binding assays revealed that F4 treatment greatly augmented the affinity and slightly increased the number of ConA binding sites in PBL. F4 also enhanced ConA-induced IL-2 receptor (Tac) expression and IL-2 production of PBL. Anti- IL-2 antibody inhibited the effect of F4 on ConA-induced proliferation. These data suggest that IL-2 is involved in augmentative effects of F4. Our results indicate that F4 is a very efficient immunopotentiator and may be used for immunotherapy.

Ectopically expressed leaf and bulb lectins from garlic (Allium sativum L.) protect transgenic tobacco plants against cotton leafworm (Spodoptera littoralis)

The insecticidal activity of the leaf (ASAL) and bulb (ASAII) agglutinins from Allium sativum L. (garlic) against the cotton leafworm, Spodoptera littoralis Boisd. (Lepidoptera: Noctuidae) was studied using transgenic tobacco plants expressing the lectins under the control of the constitutive CaMV35S promoter. PCR analysis confirmed that the garlic lectin genes were integrated into the plant genome. Western blots and semi-quantitative agglutination assays revealed lectin expression at various levels in the transgenic lines. Biochemical analyses indicated that the recombinant ASAL and ASAII are indistinguishable from the native garlic lectins. Insect bioassays using detached leaves from transgenic tobacco plants demonstrated that the ectopically expressed ASAL and ASAII significantly (P < 0.05) reduced the weight gain of 4th instar larvae of S. littoralis. Further on, the lectins retarded the development of the larvae and their metamorphosis, and were detrimental to the pupal stage resulting in weight reduction and lethal abnormalities. Total mortality was scored with ASAL compared to 60% mortality with ASAII. These findings suggest that garlic lectins are suitable candidate insect resistance proteins for the control of S. littoralis through a transgenic approach.

Arsenic-induced stress activates sulfur metabolism in different organs of garlic (Allium sativum L.) plants accompanied by a general decline of the NADPH-generating systems in roots

Arsenic (As) contamination is a major environmental problem which affects most living organisms from plants to animals. This metalloid poses a health risk for humans through its accumulation in crops and water. Using garlic (Allium sativum L.) plants as model crop exposed to 200μM arsenate, a comparative study among their main organs (roots and shoots) was made. The analysis of arsenic, glutathione (GSH), phytochelatins (PCs) and lipid peroxidation contents with the activities of antioxidant enzymes (catalase, superoxide dismutase, ascorbate-glutathione cycle), and the main components of the NADPH-generating system, including glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), NADP-malic enzyme (NADP-ME) and NADP-isocitrate dehydrogenase (NADP-ICDH) was carried out. Data showed a correlation among arsenic accumulation in the different organs, PCs content and the antioxidative response, with a general decline of the NADPH-generating systems in roots. Overall, our results demonstrate that there are clear connections between arsenic uptake, increase of their As-chelating capacity in roots and a decline of antioxidative enzyme activities (catalase and the ascorbate peroxidase) whose alteration provoked As-induced oxidative stress. Thus, the data suggest that roots act as barrier of arsenic mediated by a prominent sulfur metabolism which is characterized by the biosynthesis of high amount of PCs.

Variability of solids, organosulfur compounds, pungency and health-enhancing traits in garlic (Allium sativum L.) cultivars belonging to different ecophysiological groups

Garlic is a vegetable mainly agamically propagated, and it has been dispersed all around the world. Garlic cultivars have been classified in different ecophysiological groups (EG) according to their bulbing requirements. The variability in organosulfur composition (ACSOs), solids content (SC), pungency (PC) and antiplatelet activity (IAA) and the correlation among these traits in garlic clones belonging to three EG was studied. We found variability for ACSOs, SC, PC and IAA between clones belonging to different EG and also among clones belonging to the same EG. Cutivars EG III presented more variability than EG IV for ACSOs, thiosulfinates, allicin and PC, while for SC, EG IV was the most variable. The correlations found suggested that IAA observed was mainly due to organosulfur composition. Finally recommendations about the most suitable cultivars for fresh consumption, pharmaceutical and dehydration industry are made.

Volatile sulfur compounds in human expiration after eating raw or heat-treated garlic

Volatile sulfur compounds arising from grated raw or heat-treated garlic in both in-vitro and in-vivo tests were gas-chromatographically analyzed. In in-vitro tests, the head-space vapor gas from garlic in a vial was analyzed. It was clarified that allyl mercaptan arising from raw garlic decreased with the passage of time and other volatile low-molecular sulfur compounds (LMSC) did not show remarkable changes. The change of LMSC from heat-treated garlic was also studied. Methyl mercaptan and allyl mercaptan from heat-treated garlic gradually increased to some extent. On the other hand, the quantities of somewhat high-molecular sulfur compounds (HMSC) were much less in heat-treated garlic compared to those of raw garlic. These compounds increased till approx. 60 min and then decreased gradually. In in-vivo tests, human expiration after eating garlic was analyzed. Allyl mercaptan, methyl mercaptan and allyl methyl sulfide in LMSC were detected in significant amounts. The quantities of these compounds arising from heat-treated garlic were smaller than those from raw garlic. These compounds had the tendency of decreasing with the passage of time. On the other hand, almost no HMSC was detected in both raw and heat-treated garlic. By sensory testing, raw garlic showed a stronger smell than heat-treated garlic in both in-vitro and in-vivo tests. GC analysis exhibited higher values of volatile sulfur compounds in raw garlic. That is, the higher the volatile sulfur compound level, the stronger the garlic flavor or malodor.

Death of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in garlic butter as affected by storage temperature

Garlic is known to have antimicrobial activity against several spoilage and pathogenic bacteria. However, the fate of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in garlic butter has not been reported. This study was undertaken to determine the viability of these organisms in garlic butter as affected by the type of raw minced garlic added to the butter, storage temperature, and storage time. Unsalted butter at 40 degrees C was combined with raw minced jumbo, elephant, or small-cloved garlic at a 4:1 butter/garlic ratio (wt/wt), inoculated with mixed-strain suspensions of Salmonella, E. coli O157:H7, or L monocytogenes, and stored at 4.4, 21, or 37 degrees C for up to 48 h. All pathogens retained their viability at 4.4 degrees C, regardless of the presence of garlic. The addition of garlic to butter enhanced the rates of inactivation of all three pathogens at 21 and 37 degrees C. The most rapid decline in pathogen populations was observed at 37 degrees C. The inactivation of L. monocytogenes occurred more slowly than did that of Salmonella or E. coli O157:H7. The inactivation of Salmonella and L. monocytogenes was more rapid in jumbo garlic butter than in elephant or small-cloved garlic butter. It is concluded that Salmonella, E. coli O157:H7, and L. monocytogenes did not grow in unsalted butter, with or without garlic added (20%, wt/wt), when inoculated products were stored at 4.4, 21, and 37 degrees C for up to 48 h.

Isolation and characterization of lectins and lectin-alliinase complexes from bulbs of garlic (Allium sativum) and ramsons (Allium ursinum)

A procedure developed to separate the homodimeric and heterodimeric mannose-binding lectins from bulbs of garlic (Allium sativum L.) and ramsons (Allium ursinum L.) also enabled the isolation of stable lectin-alliinase complexes. Characterization of the individual lectins indicated that, in spite of their different molecular structure, the homomeric and heteromeric lectins resemble each other reasonably well with respect to their agglutination properties and carbohydrate-binding specificity. However, a detailed analysis of the lectin-alliinase complexes from garlic and ramsons bulbs demonstrated that only the heterodimeric lectins are capable of binding to the glycan chains of the alliinase molecules (EC 4.4.1.4). Moreover, it appears that only a subpopulation of the alliinase molecules is involved in the formation of lectin-alliinase complexes and that the complexed alliinase contains more glycan chains than the free enzyme. Finally, some arguments are given that the lectin-alliinase complexes do not occur in vivo but are formed in vitro after homogenization of the tissue.

Comparative transcriptome profiling reveals that brassinosteroid-mediated lignification plays an important role in garlic adaption to salt stress

Garlic (Allium sativum L.) is an economically important vegetable crop which is used worldwide for culinary and medicinal purposes. Soil salinity constrains the yield components of garlic. Understanding the responsive mechanism of garlic to salinity is crucial to improve its tolerance. To address this problem, two garlic cultivars differing in salt tolerance were used to investigate the long-term adaptive responses to salt stress at phenotype and transcriptome levels. Phenotypic analysis showed four-week salt stress significantly decreased the yield components of salt-sensitive cultivar. Transcriptomes of garlics were de novo assembled and mined for transcriptional activities regulated by salt stress. The results showed that photosynthesis, energy allocation, and secondary metabolism were commonly enriched in both sensitive and tolerant genotypes. Moreover, distinct responsive patterns were also observed between the two genotypes. Compared with the salt-tolerant genotype, most transcripts encoding enzymes in the phenylpropanoid biosynthesis pathway were coordinately down regulated in the salt-sensitive genotype, resulting in alternation of the content and composition of lignin. Meanwhile, transcripts encoding the enzymes in the brassinosteroid (BR) biosynthesis pathway were also systematically down regulated in the salt-sensitive genotypes. Taken together, these results suggested that BR-mediated lignin accumulation possibly plays an important role in garlic adaption to salt stress. These findings expand the understanding of responsive mechanism of garlic to salt stress.

Transcript profiling reveals an important role of cell wall remodeling and hormone signaling under salt stress in garlic

Salt stress is one of the environmental factors that evidently limit plant growth and yield. Despite the fact that understanding plant response to salt stress is important to agricultural practice, the molecular mechanisms underlying salt tolerance in garlic remain unclear. In this study, garlic seedlings were exposed to 200 mM NaCl stress for 0, 1, 4, and 12 h, respectively. RNA-seq was applied to analyze the transcriptional response under salinity conditions. A total of 13,114 out of 25,530 differentially expressed unigenes were identified to have pathway annotation, which were mainly involved in purine metabolism, starch and sucrose metabolism, plant hormone signal transduction, flavone and flavonol biosynthesis, isoflavonoid biosynthesis, MAPK signaling pathway, and circadian rhythm. In addition, 272 and 295 differentially expressed genes were identified to be cell wall and hormone signaling-related, respectively, and their interactions under salinity stress were extensively discussed. The results from the current work would provide new resources for the breeding aimed at improving salt tolerance in garlic.

Nutraceutical Applications of Garlic and the Intervention of Biotechnology

Garlic (Allium sativum L.) is an important and widely cultivated plant with both culinary and medicinal uses stemming from its biological activities, which include antibiotic, anticancer, anti-thrombotic, and lipid-lowering cardiovascular effects. Though such medicinal use of garlic existed for centuries, there was little scientific support for its therapeutic and pharmacological properties. However, there has been a recent upsurge of research on garlic aiming to understand its exact mechanism of action in each case so that garlic and its products may have more judicious future applications. Since garlic is vegetatively propagated, its improvement for desired traits through conventional means is difficult. The intervention of biotechnological methods such as tissue culture and gene transfer protocols developed recently hold great promise for improving this crop. Due to new innovations in instrumentation and processing technologies coupled with more judicious experimental models, better products are foreseen in the market. The objective of this article was to review the recent developments made towards understanding the mechanism by which garlic imparts different therapeutic effects as well as to review what biotechnology can offer to improve this crop and its products.

Assessment of genetic and epigenetic changes in virus-free garlic (Allium sativum L.) plants obtained by meristem culture followed by in vitro propagation

This is the first report assessing epigenetic variation in garlic. High genetic and epigenetic polymorphism during in vitro culture was detected.Sequencing of MSAP fragments revealed homology with ESTs. Garlic (Allium sativum) is a worldwide crop of economic importance susceptible to viral infections that can cause significant yield losses. Meristem tissue culture is the most employed method to sanitize elite cultivars.Often the virus-free garlic plants obtained are multiplied in vitro (micro propagation). However, it was reported that micro-propagation frequently produces somaclonal variation at the phenotypic level, which is an undesirable trait when breeders are seeking to maintain varietal stability. We employed amplification fragment length polymorphism and methylation sensitive amplified polymorphism (MSAP) methodologies to assess genetic and epigenetic modifications in two culture systems: virus-free plants obtained by meristem culture followed by in vitro multiplication and field culture. Our results suggest that garlic exhibits genetic and epigenetic polymorphism under field growing conditions. However, during in vitro culture system both kinds of polymorphisms intensify indicating that this system induces somaclonal variation. Furthermore, while genetic changes accumulated along the time of in vitro culture, epigenetic polymorphism reached the major variation at 6 months and then stabilize, being demethylation and CG methylation the principal conversions.Cloning and sequencing differentially methylated MSAP fragments allowed us to identify coding and unknown sequences of A. sativum, including sequences belonging to LTR Gypsy retrotransposons. Together, our results highlight that main changes occur in the initial 6 months of micro propagation. For the best of our knowledge, this is the first report on epigenetic assessment in garlic.

Regression of preestablished cholesterol gallstones by dietary garlic and onion in experimental mice

We have recently reported the health beneficial potential of dietary garlic and onion in reducing the incidence and severity of cholesterol gallstone (CGS) during its experimental induction in mice. In the current study, the efficacy of dietary garlic and onion in regressing preestablished CGS was investigated in experimental mice. After inducing CGS in mice with a lithogenic diet for 10 weeks, they were maintained on basal diets containing 0.6% dehydrated garlic or 2% dehydrated onion for a further 10 weeks. Dietary garlic and onion, either raw or heat processed, regressed preformed CGS in mice up to 53% to 59%, whereas the regression in the basal control diet group was only 10%. The antilithogenic potency of garlic was decreased by its heat processing, but not in the case of onion. Biliary cholesterol was significantly decreased in garlic- and onion-fed animals. Biliary cholesterol saturation index and hydrophobicity index were significantly lowered by dietary garlic and onion. Serum and liver cholesterol levels were decreased by feeding these spices during post-CGS induction period. Hepatic hydroxymethylglutaryl-coenzyme A reductase activity was increased after feeding garlic and onion, whereas activities of the cholesterol-degrading enzymes cholesterol-7α-hydroxylase and sterol-27-hydroxylase were increased in spice-fed groups. These results indicate that feeding garlic and onion effectively accelerates the regression of preformed CGS by promoting cholesterol desaturation in bile. This observation is significant in the context of evolving dietary intervention strategy to address regression of existing CGS and stopping the possible recurrence.

Mustard oil and garlic extract as inhibitors of sodium arsenite-induced chromosomal breaks in vivo

Arsenic, a well-known human carcinogen present as a contaminant in ground water poses a serious threat to public health in various countries. The anticlastogenic properties of two dietary supplements, garlic and mustard oil, were screened against the clastogenic activity of sodium arsenite, since diet may contain factors which affect the process of mutagenesis and carcinogenesis. Aqueous extract of garlic (100 mg/kg b.w.) and mustard oil (0.643 mg/kg b.w.) were fed to Mus musculus for 30 consecutive days either singly or simultaneously. Sodium arsenite (0.1 mg/kg b.w.) was injected subcutaneously on days 7, 14, 21 and 30 of the experiment, singly and together with the dietary supplements. The animals were sacrificed 24 h after the last exposure to sodium arsenite and clastogenic effects were observed in the bone marrow cells. The degree of modulation of sodium arsenite-induced chromosomal aberrations was more pronounced in mustard oil than in garlic extract and simultaneous administration of both the dietary supplements reduced the clastogenic effects of sodium arsenite closer to the level of the negative control. The greater efficacy could be due to the interaction of the two dietary supplements and its radical scavenging property.

Comprehensive Metabolite Profiling in Genetic Resources of Garlic (Allium sativum L.) Collected from Different Geographical Regions

Garlic (Allium sativum) is the second most important Allium crop that has been used as a vegetable and condiment from ancient times due to its characteristic flavor and taste. Although garlic is a sterile plant that reproduces vegetatively through cloves, garlic shows high biodiversity, as well as phenotypic plasticity and environmental adaptation capacity. To determine the possible mechanism underlying this phenomenon and to provide new genetic materials for the development of a novel garlic cultivar with useful agronomic traits, the metabolic profiles in the leaf tissue of 30 garlic accessions collected from different geographical regions, with a special focus on the Asian region, were investigated using LC/MS. In addition, the total saponin and fructan contents in the roots and cloves of the investigated garlic accessions were also evaluated. Total saponin and fructan contents did not separate the garlic accessions based on their geographical origin, implying that saponin and fructan contents were clone-specific and agroclimatic changes have affected the quantitative and qualitative levels of saponins in garlic over a long history of cultivation. Principal component analysis (PCA) and dendrogram clustering of the LC/MS-based metabolite profiling showed two major clusters. Specifically, many Japanese and Central Asia accessions were grouped in cluster I and showed high accumulations of flavonol glucosides, alliin, and methiin. On the other hand, garlic accessions grouped in cluster II exhibited a high accumulation of anthocyanin glucosides and amino acids. Although most of the accessions were not separated based on country of origin, the Central Asia accessions were clustered in one group, implying that these accessions exhibited distinct metabolic profiles. The present study provides useful information that can be used for germplasm selection and the development of new garlic varieties with beneficial biotic and abiotic stress-adaptive traits.

Influence of garlic compared to aspirin on induced photothrombosis in mouse pial microvessels, in vivo

Effect of garlic on photochemically-induced platelet aggregation in pial microvessels of the mouse, in vivo, was compared to that of acetyl salicylic acid (ASA). Three trials were carried out, in which garlic at doses of 12.5, 25, 50 and 100 mg/kg and ASA doses of 25, 50 and 100 mg/kg were used. Each trial included treatment groups of male mice, approximately 30 g, and a control group. Animals were anesthetized (urethane, 1-2 mg/g, i.p.), the trachea was intubated and a craniotomy was performed. Induction of platelet aggregation was made by activation of circulating sodium fluorescein (0.1 ml of 5% solution/25 g, i.v.) with an intense mercury light. Garlic, ASA and vehicle solutions were injected, i.p., 60 min prior to the photochemical insult. The time for the first platelet aggregate to appear in pial arterioles was significantly delayed (P < 0.001) only by the 100 mg/kg garlic dose and by all ASA doses. The effect of this garlic dose on first aggregate was comparable to that of the 25 and 50 mg/kg ASA doses. Only the ASA doses delayed (P < 0.05) the appearance of first aggregate in venules. Arteriolar and venular diameter changes were not different among groups of all trials. Data of this study documented that garlic was capable of delaying platelet aggregation in mouse pial arterioles, in vivo.

Tubulin cytoskeleton during microsporogenesis in the male-sterile genotype of Allium sativum and fertile Allium ampeloprasum L

KEY MESSAGE

Microsporogenesis in garlic. The male-sterile Allium sativum (garlic) reproduces exclusively in the vegetative mode, and anthropogenic factors seem to be the cause of the loss of sexual reproduction capability. There are many different hypotheses concerning the causes of male sterility in A.sativum; however, the mechanisms underlying this phenomenon have not been comprehensively elucidated.Numerous attempts have been undertaken to understand the causes of male sterility, but the tubulin cytoskeleton in meiotically dividing cells during microsporogenesis has never been investigated in this species. Using sterile A.sativum genotype L13 and its fertile close relative A. ampeloprasum (leek), we have analysed the distribution of the tubulin cytoskeleton during microsporogenesis. We observed that during karyokinesis and cytokinesis, in both meiotic divisions I and II, the microtubular cytoskeleton in garlic L13 formed configurations that resembled tubulin arrangement typical of monocots. However, the tubulin cytoskeleton in garlic was distinctly poorer (composed of a few MT filaments) compared with that found in meiotically dividing cells in A. ampeloprasum. These differences did not affect the course of karyogenesis, chondriokinesis, and cytokinesis, which contributed to completion of microsporogenesis, but there was no further development of the male gametophyte. At the very beginning of the successive stage of development of fertile pollen grains, i.e. gametogenesis, there were disorders involving the absence of a normal cortical cytoskeleton and dramatically progressive degeneration of the cytoplasm in garlic. Therefore,we suggest that, due to disturbances in cortical cytoskeleton formation at the very beginning of gametogenesis, the intracellular transport governed by the cytoskeleton might be perturbed, leading to microspore decay in the male-sterile garlic genotype.

Development of alternative plant vitrification solutions in droplet-vitrification procedures

This study aimed at developing alternative vitrification solutions, modified either from the original PVS2 vitrification solution by increasing glycerol and sucrose and/or decreasing dimethylsulfoxide and ethylene glycol concentration, or from the original PVS3 vitrification solution by decreasing glycerol and sucrose concentration. The application of these vitrification solutions to two model species, i.e. garlic and chrysanthemum in a droplet-vitrification procedure, revealed that PVS3 and variants were superior to PVS2 and variants and that most PVS2 variants were comparable to the original PVS2. Both species were sensitive to chemical toxicity of permeating cryoprotectants and chrysanthemum was also sensitive to osmotic stress. The lower recovery of cryopreserved garlic shoot apices dehydrated with PVS2 and variants compared with those dehydrated with PVS3 and variants seemed attributed to cytotoxicity of the vitrification solutions tested as well as to insufficient protection against freezing injury. Chrysanthemum shoot tips were very sensitive to both chemical toxicity and osmotic stress and therefore, induction of cytotoxity tolerance during preconditioning was required for successful cryopreservation. The present study revealed that some of the PVS2 variants tested which have increased glycerol and sucrose and/or decreased dimethylsulfoxide and ethylene glycol concentration can be applied when explants are of medium size, tolerant to chemical toxicity and moderately sensitive to osmotic stress. PVS3 and variants can be used widely when samples are heterogeneous, of large size and/or very sensitive to chemical toxicity and tolerant to osmotic stress.

Induction of reactive oxygen species and the potential role of NADPH oxidase in hyperhydricity of garlic plantlets in vitro

Hyperhydricity is a physiological disorder associated with oxidative stress. Reactive oxygen species (ROS) generation in plants is initiated by various enzymatic sources, including plasma membrane-localized nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, cell wall-bound peroxidase (POD), and apoplastic polyamine oxidase (PAO). The origin of the oxidative burst associated with hyperhydricity remains unknown. To investigate the role of NADPH oxidases, POD, and PAO in ROS production and hyperhydricity, exogenous hydrogen peroxide (H2O2) and inhibitors of each ROS-producing enzyme were applied to explore the mechanism of oxidative stress induction in garlic plantlets in vitro. A concentration of 1.5 mM H2O2 increased endogenous ROS production and hyperhydricity occurrence and enhanced the activities of NADPH oxidases, POD, and PAO. During the entire treatment period, NADPH oxidase activity increased continuously, whereas POD and PAO activities exhibited a transient increase and subsequently declined. Histochemical and cytochemical visualization demonstrated that specific inhibitors of each enzyme effectively suppressed ROS accumulation. Moreover, superoxide anion generation, H2O2 content, and hyperhydric shoot frequency in H2O2-stressed plantlets decreased significantly. The NADPH oxidase inhibitor was the most effective at suppressing superoxide anion production. The results suggested that NADPH oxidases, POD, and PAO were responsible for endogenous ROS induction. NADPH oxidase activation might play a pivotal role in the oxidative burst in garlic plantlets in vitro during hyperhydricity.

Cytological and biophysical comparative analysis of cell structures at the microsporogenesis stage in sterile and fertile Allium species

Using a live-cell-imaging approach and autofluorescence-spectral imaging, we showed quantitative/qualitative fluctuations of chemical compounds within the meiocyte callose wall, providing insight into the molecular basis of male sterility in plants from the genus Allium. Allium sativum (garlic) is one of the plant species exhibiting male sterility, and the molecular background of this phenomenon has never been thoroughly described. This study presents comparative analyses of meiotically dividing cells, which revealed inhibition at the different microsporogenesis stages in male-sterile A. sativum plants (cultivars Harnas and Arkus) and sterile A. ampeloprasum var. ampeloprasum (GHG-L), which is phylogenetically related to garlic. Fertile species A. ampeloprasum (leek) was used as the control material, because leek is closely related to both garlic and GHG-L. To shed more light on the molecular basis of these disturbances, autofluorescence-spectral imaging of live cells was used for the assessment of the biophysical/biochemical differences in the callose wall, pollen grain sporoderm, and the tapetum in the sterile species, in comparison with the fertile leek. The use of techniques for live-cell imaging (autofluorescence-spectral imaging) allowed the observation of quantitative/qualitative fluctuations of autofluorescent chemical compounds within the meiocyte callose wall. The biophysical characterisation of the metabolic disturbances in the callose wall provides insight into the molecular basis of male sterility in A. sativum. In addition, using this method, it was possible for the first time, to determine precisely (on the basis of fluctuations of autofluorescence compounds) the meiosis stage in which normal microsporogenesis is disturbed, which was not visible using light microscopy.

Analysis of interferograms of multi-layered biological samples obtained from full field optical coherence tomography systems

Several methods were developed in the past to analyze interferograms produced by optical coherence tomography, and successfully applied to simulated or animated samples. However, these techniques do not cope with noisy and distorted interferograms from biological tissues. In this paper, known techniques, including the fast Fourier transform and several variations of the continuous wavelet transform, were employed to analyze the interferogram data. However, to cope with the difficulties in biological data, pre- and post-processing procedures and adaptive thresholding were developed to provide stability and robustness. Additionally, three-dimensional structural models of the biological samples were constructed, and revealed information like the number and locations of interfaces, the layer thickness and pattern, and abnormalities.